Most of currently promising molecular-targeted drugs against cancer are receptor tyrosine kinase inhibitors such as erlotinib and lapatinib. Many of them are highly effective against cancers with mutation, amplification, or overexpression of target genes. However, such molecular-targeted agents cannot exert efficacy against cancers in which genes that are not their targets are altered. Thus, there is still no established therapeutic method that is effective against such cancers. Inhibitors against novel genes altered in cancer are expected to make a great contribution to treatment of cancer patients on whom conventional drugs have no effect.
Fibroblast growth factor receptors (FGFRs) are kinases belonging to the receptor tyrosine kinase family. FGFR1, FGFR2, FGFR3, and FGFR4 constitute the FGFR family. The ligand is fibroblast growth factor (FGF), and 22 types of structurally similar proteins form a family. It is known that each FGFR is activated upon overexpression, gene amplification, mutation, or translocation, and serves as a cause of cancer. The FGFR signal follows the MAPK pathway or PI3K/AKT pathway. In cancer, the signal is known to be involved in cell growth, angiogenesis, cell migration, invasion, metastasis, and such (Non-patent Document 1).
The FGFR1 gene is known to be amplified in breast cancer and non-small cell lung cancer (Non-patent Documents 2 and 3); mutated in glioblastoma (Non-patent Document 4); translocated to generate a fusion protein in acute myelocytic leukemia (Non-patent Document 5); and overexpressed in pancreatic cancer, bladder cancer, prostatic cancer, and esophageal cancer. Furthermore, FGFR1 is known to be expressed in neovessels and greatly contribute to angiogenesis (Non-patent Document 6). The FGFR2 gene is known to be amplified in stomach cancer and breast cancer (Non-patent Documents 7 and 8); mutated in endometrial cancer (Non-patent Document 9); and overexpressed in prostatic cancer, esophageal cancer, ovarian cancer, pancreatic cancer, brain tumor, and colon cancer. The FGFR3 gene is known to be translocated in multiple myeloma (Non-patent Document 10); mutated in bladder cancer (Non-patent Document 11); and overexpressed in ovarian cancer, non-small cell lung cancer, and hepatocellular carcinoma. Finally, FGFR4 is known to be mutated in lung cancer, ovarian cancer, prostatic cancer, etc.; and overexpressed in thyroid cancer, ovarian cancer, etc.
As described above, all FGFR family kinases have been strongly suggested to be involved in cancer. Thus, the inhibition of the FGFR family kinases in cancer tissues may be a promising therapeutic method for treating the above types of cancer.